Starting tomorrow, January 16th, Windows 8.1 Preview will restart every two hours once and you will lose any unsaved data during this restart.

If you’re running Windows 8.1 Preview, you probably have seen “Reinstall Windows Now. Your license to use this evaluation version of Windows will expire soon. When it expires, your PC will restart every two hours. Get the latest version of Windows to avoid these interruptions” notice every time you log in.

Windows 8.1 Preview users can easily upgrade to the RTM by clicking on the Get Windows button when you see the Reinstall Windows Now notice. Alternatively, you can visit the Windows Store to download and install the update.

And if your PC was running Windows 8 before upgrading to Windows 8.1 Preview, you might be able to revert to Windows 8 by running Refresh PC tool. In this case, you can retain your personal data but apps that you had installed from the Store will need to be reinstall.